The thermionic power generator which transforms thermal energy into the electrical energy is known by capturing the thermoelectron emitted from an emitter electrode by the collector electrode (see the patent document 1 listed below).
(Patent document 1) JP 2004-349398 A
However, since the amount of the thermoelectron emitted from an emitter electrode is dependent on the temperature of the heat source which touches an emitter electrode, the temperature of this heat source is uncontrollable by a thermionic power generator given in the above-mentioned patent document 1.